Laser machining presentation based on liming he et al paper
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This document analyzes the optimization of wavelengths for machining metals using harmonic generations of a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. It calculates the absorption efficiency of various metals at different harmonic wavelengths by determining the absorptivity of each metal and the conversion efficiency of the nonlinear optical crystals used to generate the harmonics. The results show that for metals like gold, silver, and copper, the optimum machining wavelengths are the third, fourth, and second harmonics respectively, while for metals like nickel and platinum it is the fundamental Nd:YAG wavelength. Experimental validation on gold substrates confirms the calculated optimum wavelengths.
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Laser machining presentation based on liming he et al paper
- 1. LASERS: Nd:YAG MACHINING Wavelength optimization for machining metals with the harmonic generations of a short pulsed Nd:YAG laser Liming He, Yoshiharu Namba, Yuji Narita Received: 23rd August 1999 Revised: 13th December 1999 Accepted: 27th December 1999
- 2. Introduction – Laser machining • Highly coherent light is directed towards the w/p for machining • Lasers of different wavelengths are used in machining variety of materials • It is important to select the optimum wavelength of laser beam for machining various materials • Why lasers: • a) monochromatic • b) Parallel • Therefore, can be focused to a very small diameter generating energy (as high as 100 MV/ mm2 WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 3. Introduction- Nd:YAG Laser • Neodymium-doped yttrium aluminum garnet • Yttrium aluminium garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. • Garnets are a group of silicate minerals • Garnets possess similar physical properties and crystal forms but different chemical compositions. The different species are pyrope, almandine, spessartine, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series: pyrope-almandine-spessarite and uvarovite-grossular-andradite. • Produces a collimated coherent beam in the near infrared region of λ= 1064 nm • Can be run pulsed or continuously • Solid- state laser, safe to use and does not produce noxious gas • Can be made small in size and low in cost • Fundamental harmonic laser converted to higher harmonics by use of nonlinear optical crystals WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 4. Introduction- Nonlinear optical crystals • Dielectric polarization responds non-linearly, P, to the electric field, E, of the light • Examples: Potassium titanyl Phosphate (KTP), Potassium dihydogen phosphate (KDP), Cesium dihydroarsenate (CDA) etc. • Properties • Strongly bifringent (necessary to obtain phase matching) • Have specific crystal symmetry • High damage threshold which make them resistant to high intensity laser light WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 5. Presentation statement • An analytical method of wavelength optimization for machining metals with various harmonic generations of a Nd:YAG • From Absorptivity of metal and the conversion efficiency of laser apparatus, absorptivity efficiency is estimated for selecting an optimum machining wavelength • As examples Gold, Silver, Copper, Nickel etc. are examined, and their optimum machining wavelengths are obtained WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 6. Absorption η for different H.G of a Nd:YAG • Conversion η λ1 Nd:YAG • • • • • λ1 Nonlinear crystal λ4 Filter λ2 The first, second, third and fourth-harmonic lasers from a Nd:YAG resonator by using nonlinear optical crystals λ1 – 1064 nm fundamental harmonic wavelength λ2 – 532 nm- second harmonic wavelength obtained by use of KTP crystals λ3 - 355 nm- third harmonic wavelength obtained by use of KDP crystals λ4 – 266 nm - fourth harmonic wavelength obtained by use of CDA crystals WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 8. Conversion η • The third harmonic is obtained from fundamental generation of second harmonic: ω +2ω ω • Fourth harmonic is generated from fundamental generation of second harmonic: 2ω +2ω 4ω • The output laser energy of the harmonic generations are measured with a power meter • With the obtained data conversion η of the various harmonic generations can be estimated with equation 1 WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 9. Results • 41%, 25%, 13% for KTP, KD*P and CD*A respectively WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 13. • It is evident that for most metals absorptivity are high in short wavelength region • More energetic photons can be absorbed by a greater number of bound electrons in shorter wavelength region, the reflectivity falls at shorter wavelengths, and the absorptivity of surface is increased in the region of short wavelength. WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 15. Results: Tables 2 and 3 λ/ Materials 213 nm 266 nm 355 nm 532 nm 1064 nm Gold 73. 85 63.78 63.66 23.47 2.05 Silver 73.54 74.04 23.36 4.50 2.59 Copper 61.2 66.28 58.03 38.93 2.75 Nickel 58.15 57.49 57.35 40.08 27.41 Molybdenum 31.50 33.69 45.69 41.63 32.44 Platinum 70.64 58.92 48.26 50.40 25.18 λ/ Materials 213 nm 266 nm 355 nm 532 nm 1064 nm Gold 4.80 8.29 15.92 9.62 2.05 Silver 4.78 9.63 5.82 1.85 2.59 Copper 3.98 8.62 14.51 16.43 27.41 Nickel 3.78 7.47 14.34 16.43 27.41 Molybdenum 2.05 4.38 11.42 17.07 32.44 Platinum 4.59 7.66 12.06 20.66 25.18 WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 16. Experimental Results and Discussions • • • • Experimental setup: Laser beam properties; diameter 6.0 mm Duration pulses: 10-12 ns Wavelengths: 1064 nm, 532 nm, 355 nm, and 266 nm using nonlinear crystals KTP, KD*P and CD*A for frequency generation respectively • Results in table 3 were verified by machining gold as an experimental substrate • Input fluence was varied from 0 to 500 J/cm2 WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 17. Results • Machined result is consistent with calculated results • η is an aggregate parameter for examining machining parameter WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 18. • The absorptivity of materials for various harmonic generations of a Nd:YAG laser are definite and unchangeable • Conversion efficiencies are changeable because of using different nonlinear crystals or using different laser fluences • For the same material, the maximum absorption efficiency may be different, because various laser apparatus are used. WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT
- 19. Conclusions • Optimum machining wavelength can be estimated by calculating the absorption efficiency • For the various metals, the optimum machining wavelength are different • Gold, silver and copper their highest absorption efficiencies are the 3rd, 4th and 2nd harmonic generations respectively • Nickel, platinum, and others optimum machining wavelengths are all in the fundamental wavelengths of the Nd:YAG laser WACHIRA J. NDUNG'U/MEMS/MECHATRONIC ENGINEERING/JKUAT